Addition Of Chemical Modifier Research Articles

Inside Back Cover

The inside back cover picture showed the liquid‐liquid interface (LLI) self‐assembly structure as a new substrate for analytical sensing. There were two methods to promote self‐assembly at the LLI. On the one hand, strategies for promoting assembly of NPs at the LLI have been developed through the addition of chemical modifiers, promoters, or external voltage. On the other hand, in order to avoid the potential interferences of chemical promoters, shaking organic solution and aqueous solution was proposed as an alternative way to form uniform NPs array at the LLI based on emulsification mechanism. Such strategies to fabricate uniform SERS substrate based on the LLI were demonstrated to be efficient to improve the reproducibility of SERS analysis, which are potentially applicable for practical applications. More details are discussed in the article by Zhang et al. on page 569—580.image

Highly sensitive determination of mercury by improved liquid cathode glow discharge with the addition of chemical modifiers

The sample introduction system of early miniaturized liquid cathode glow discharge (LCGD) was improved, and then LCGD was used as an excitation source of atomic emission spectrometry (AES) for the detection of mercury in water samples. The effects of chemical modifiers, such as ionic surfactants and low molecular weight organic substances, on emission intensities of Hg were investigated. The results showed that the addition of 4% methanol and 0.15% hexadecyltrimethylammonium bromide (CTAB) can enhance the net intensity of Hg about 15.5-fold and 7.7-fold, and the sensitivity (S) of Hg about 15.2-fold and 5.6-fold, respectively. Adding chemical modifiers markedly reduce the interferences from Fe3+, Co2+, Cl−, Br−, and I− ions. The limit of detection (LOD) is reduced from 0.35 mg L−1 for no chemical modifier to 0.03 mg L−1 for 4% methanol and 0.05 mg L−1 for 0.15% CTAB. The relative standard deviation (RSD) of Hg with adding 4% methanol, 0.15% CTAB and no chemical modifier is 2.38%, 1.17% and 3.00%, respectively, and the power consumption is below 75 W. All results indicated that the determination of Hg using improved LCGD with the addition of chemical modifiers has high sensitivity, low LOD, well precision and low power consumption. Water samples containing high mercury (10–20 mg L−1) and low mercury (0.2–5 mg L−1) can be determined by improved LCGD-AES with no chemical modifier and 4% methanol, respectively. Adding 4% methanol significantly reduces the matrix effects from real water samples. The measurement results of spiked samples using LCGD-AES are largely consistent with the spiked value. In addition, the recoveries of Hg are ranged from 95.7% to 114.8%, suggesting that the measurement results of Hg by LCGD-AES are accurate and reliable. Overall, the improved LCGD-AES with adding chemical modifiers is a promising technique for on-site and real-time monitoring of Hg in water samples because of its portability, lower cost and speed.

MS/MSALL with SelexION®: A High‐throughput Lipidomic Solution for Untargeted Profiling

Global lipid profiling is a growing area of interest and is a primary means to measure the changes in lipid molecular species as a function of human disease or drug treatment. One of the most challenging aspects of lipid analysis by mass spectrometry is isobaric overlap, or molecules having the same or nearly the same mass. With direct infusion, or ‘Shotgun’ approaches, the user is able to rapidly profile biological samples. On the Sciex 6600+ TripleTOF®, the MSMSALL method on this system generates data by collecting product ions of all precursor masses. Using this approach, thousands of lipids can be represented in a profile snapshot and allows for retrospective analysis of acquired data. However the issue of isobaric overlap is not addressed.Isobaric overlap is a complex problem in lipidomic workflows and can make positive identification or quantification of a lipid species very difficult. The issue of isobaric overlap is often approached with liquid chromatography separation. However, lengthy sample preparation, method development, and lengthy chromatographic run times for adequate separation can narrow the scope of the lipidome and diminish throughput. Differential ion mobility separation (DMS) is a relatively new ion mobility technology that uses a molecule’s dipole moment to isolate it rather than shape and size. The SelexION® device is installed at atmosphere, so the addition of chemical modifiers can be applied to the system to assist in additional separation. In this study, 1‐propanol is used as the chemical modifier to separate the six phospholipid subclasses while cardiolipin’s ‐2H charge state is used to separate this class without the assistance of chemical modifier. Unique compensation voltages are then found with standards and assigned to each lipid class to ensure lipid class isolation. In negative ion mode, all seven classes can be acquired in just under twelve minutes of total run time. This allows for untargeted, high‐throughput acquisition of the lipidome while simultaneously acquiring MS/MS spectra for lipid species identification.LipidView software is used to analyze the data collected from the SelexION® runs in a high throughput fashion. All samples from each class can be loaded and a lipid class can be assigned along with its corresponding COV. Since much of the isobaric overlap has been removed from the sample a positive identification and quantification can be made.

Determination of trace cadmium in zinc concentrate by liquid cathode glow discharge with a modified sampling system and addition of chemical modifiers for improved sensitivity

In this work, a sampling system of liquid cathode glow discharge (LCGD) was developed for the highly sensitive determination of Cd in digested Zn concentrate samples, in which buffer bottle was used to eliminate the pulsation of peristaltic pump and increase the stability of discharge, and six-port valve injection system was employed to ensure the continuity of discharge and improve the precision and speed of analysis. The results showed that the flow rate of modified LCGD is reduced to 2.4 mL min−1 from the previous 4.5 mL min−1. The presence of anions and cations does not significantly interfere with the detection of Cd. Compared with the addition of no chemical modifier, the net intensity of Cd with 0.15% hexadecyltrimethylammonium bromide (CTAB) and 18% formic acid is improved by 2.4- and 2.7-fold, respectively. The relative standard deviations with 18% formic acid, 0.15% CTAB and no chemical modifier are 0.87%, 2.01% and 2.39%, respectively. The sensitivity of Cd is improved with the addition of chemical modifiers by factors of 4.5 for 18% formic acid and 2.6 for 0.15% CTAB. The LOD with 18% formic acid for Cd is arrived at 0.0049 mg L−1 which improved by 2.7 times. The results measured by modified LCGD-AES are in accordance with the reference value as well as verification values measured by ICP-AES. In addition, the recoveries are in the range of 96.5–105.4%. The accuracy, reliability and practicality can satisfy the requirements of monitoring of trace Cd in complex samples.

Preferential Ion Microsolvation in Mixed-Modifier Environments Observed Using Differential Mobility Spectrometry.

The preferential solvation behavior for eight different derivatives of protonated quinoline was measured in a tandem differential mobility spectrometer mass spectrometer (DMS-MS). Ion-solvent cluster formation was induced in the DMS by the addition of chemical modifiers (i.e., solvent vapors) to the N2 buffer gas. To determine the effect of more than one modifier in the DMS environment, we performed DMS experiments with varying mixtures of water, acetonitrile, and isopropyl alcohol solvent vapors. The results show that doping the buffer gas with a binary mixture of modifiers leads to the ions binding preferentially to one modifier over another. We used density functional theory to calculate the ion-solvent binding energies, and in all cases, calculations show that the quinolinium ions bind most strongly with acetonitrile, then isopropyl alcohol, and most weakly with water. Computational results support the hypothesis that the quinolinium ions bind exclusively to whichever solvent they have the strongest interaction with, regardless of the presence of other modifier gases.

Effects of chemical modifications on the rheological and the expansion behavior of polylactide (PLA) in foam extrusion

AbstractIt is well known that polylactide (PLA) is difficult to foam due to its low melt strength. Thus, many ways were described in the literature to enhance the foamability. However, the melt strength was actually determined only in a limited number of publications. In this study, the addition of chemical modifiers was used to change the rheological behavior of PLA and thereby improve its foamability in foam extrusion process. For the first time the use of dicumyl peroxide modified PLA in foam extrusion is described. Both modifications lead to a distinct increase in melt strength. Here, the highest increase was shown for the PLA modified with dicumyl peroxide. Furthermore, strain hardening was observed for PLA modified with the peroxide. Low density foams were achieved for neat and modified PLA in foam extrusion. Neat PLA showed a density of 45 kg/m3, while the peroxide modified PLA showed the highest expansion with a density reduction down to 32 kg/m3. Both modifications result in a more uniform cell structure and an improved compression strength. Here, the foamed, peroxide modified PLA showed outstanding performance compared to neat PLA foam with twice the compression strength (151 Pa) even at a 30% lower density.

Preparation of a finely patterned La1.89Ce0.11CuO4-x film via chemical modification

In this paper, three La1.89Ce0.11CuO4-x (LCCO) photosensitive sols were prepared with benzoylacetone (BzAcH), acetylacetone (AcAc) or 2,2′-bipyridine (BPY) as the chemical modifiers. UV absorption spectroscopy was employed to analyze the chelation mechanism of three chemical modifiers and metal ions in the sols. It has been found that the copper ions chelated with the chemical modifiers mentioned above and endowed ultraviolet photosensitivity to the sol, whereas the lanthanum ions and cerium ions did not chelate with the chemical modifiers. UV irradiation experiments indicated that the chelate compounds were decomposed and the decomposition products greatly reduced the solubility of LCCO gel films in the organic solvent. The LCCO films with fine structure were fabricated by using self-photosensitive property of the three gel films. The micro-machining process showed that LCCO fine patterns, prepared by the sol of BzAcH as the chemical modifiers, exhibited the highest precision and the minimum size of the prepared patterns reached to micron level. XRD patterns seen that the addition of chemical modifiers had no effect on the structure of LCCO inorganic film. R-T curve tests of fine-patterned LCCO films prepared with the above three sols revealed that the micro-machining method was a simple and cost-effective process, which did not influence the electrical properties of the LCCO films.

High purity polyimide analysis by solid sampling graphite furnace atomic absorption spectrometry

In this work, Cr, Cu, Mn, Na and Ni were determined in high purity polyimides (99.5%) by solid sampling graphite furnace atomic absorption spectrometry (SS-GFAAS) using Zeeman effect background correction system with variable magnetic field, making possible the simultaneous measurement at high or low sensitivity. The following analytical parameters were evaluated: pyrolysis and atomization temperatures, feasibility of calibration with aqueous solution, linear calibration range, sample mass range and the use of chemical modifier. Calibration with aqueous standard solutions was feasible for all analytes. No under or overestimated results were observed and up to 10mg sample could be introduced on the platform for the determination of Cr, Cu, Mn, Na and Ni. The relative standard deviation ranged from 3 to 20%. The limits of detection (LODs) achieved using the high sensitivity mode were as low as 7.0, 2.5, 1.7, 17 and 0.12ngg−1 for Cr, Cu, Mn, Na and Ni, respectively. No addition of chemical modifier was necessary, except for Mn determination where Pd was required. The accuracy was evaluated by analyte spike and by comparison of the results with those obtained by inductively coupled plasma optical emission spectrometry and inductively coupled plasma mass spectrometry after microwave-assisted digestion in a single reaction chamber system and also by neutron activation analysis. No difference among the results obtained by SS-GFAAS and those obtained by alternative analytical methods using independent techniques. SS-GFAAS method showed some advantages, such as the determination of metallic contaminants in high purity polyimides with practically no sample preparation, very low LODs, calibration with aqueous standards and determination in a wide range of concentration.

Heat transfer during solidification of chemically modified Al–Si alloys around a copper chill

The solidifying metal/chill contour will significantly affect the boundary heat transfer coefficients, and solidification modellers should be aware of the casting conditions for which the heat transfer coefficients are determined. The previous work carried out on solidification of Al–Si alloys in a metallic mould and solidification against bottom/top chills has shown that modification and chilling have synergetic effect resulting in a significant increase in the heat flux transients at the casting/chill interface. In the present work, the heat transfer during solidification of unmodified and chemically modified Al–Si alloys around a cylindrical copper chill was investigated. Heat flux transients were estimated using lumped heat capacitance method. Lower peak heat flux was obtained with chemically modified alloy. This is in contrast to the results reported for alloys solidifying against chills and in metallic moulds. The chill thermal behaviour and heat transfer to the chill material when surrounded by modified and unmodified alloys were explained on the basis of the decrease in the degree of undercooling in the case of modified alloy as compared to unmodified alloy and the change in contact condition and shrinkage characteristics of the alloy due to the addition of chemical modifiers.

Direct determination of Cu and Fe in jet fuel by electrothermal atomic absorption spectrometry with injection of sample as detergent emulsions

This paper reports the development of a method for the determination of copper and iron in jet fuels employing the electrothermal atomic absorption spectrometry (ETAAS). In order to allow the direct determination of the analytes, the samples were injected into the graphite furnace as detergent emulsions in order to avoid their volatilization during analysis. The results obtained in this work indicated that a stable emulsion can be formed by mixing 1mL of a 7% m/v Triton X-100 solution containing 10% v/v HNO3 with 4mL of jet fuel. The injection of emulsions provided integrated absorbance signals with suitable sensitivity and precision for 300min at least. The addition of chemical modifier was not necessary because background values were always very low, allowing the use of pyrolysis temperature around 1000°C for both analytes. Both Triton X-100 and HNO3 concentrations in the solution used to form the emulsion had remarkable influence on the sensitivity as well as the heating rate employed in the drying step. Under the best conditions established in the present work, limits of detection of 0.50 and 0.46μgL−1 were observed for copper when oil-based and aqueous standards were added to the emulsions for calibration, respectively. For iron, the limits of detection were 0.88 and 0.90μgL−1 for oil-based and aqueous standards, respectively. The method was applied in the determination of Cu and Fe in five samples of jet fuels and a recovery test was performed, producing recovery percentages between 95% and 105%.

Fuel Analysis by Filter Furnace Electrothermal Atomic Absorption Spectrometry

Abstract The determination of Mn, Fe, Co, and Zn was performed in gasoline, jet, and diesel fuel samples by electrothermal atomic absorption spectrometry using the Transverse Heated Filter Atomizer (THFA). Thermal conditions were experimentally defined for the investigated elements. The elements were analyzed without the addition of chemical modifiers, using organometallic standards for the calibration. Gasoline samples were analyzed directly, while jet and diesel fuel samples were diluted 1+3 with n-heptane. The following LODs were obtained using 40 µL injections: 0.08 µg/L Mn, 0.35 µg/L Fe, 0.54 µg/L Co, and 0.06 µg/L Zn. The limits of determination, calculated for diesel and jet fuel samples, were 1.2 µg/kg Mn, 4.9 µg/kg Fe, 7.6 µg/kg Co, and 0.8 µg/kg Zn. The corresponding limits of quantitation for gasoline samples were about four times higher.

The surface chemistry of heterogeneous catalysis: Mechanisms, selectivity, and active sites

The role of chemical kinetics in defining the requirements for the active sites of heterogeneous catalysts is discussed. A personal view is presented, with specific examples from our laboratory to illustrate the role of the chemical composition, structure, and electronic properties of specific surface sites in determining reaction activity and selectivity. Manipulation of catalytic behavior via the addition of chemical modifiers and by tuning of the reaction conditions is also introduced.

Determination of trace elements in automotive fuels by filter furnace atomic absorption spectrometry

The determination of Cd, Cr, Cu, Pb and Ni was performed in gasoline and diesel fuel samples by electrothermal atomic absorption spectrometry using the Transverse Heated Filter Atomizer (THFA). Thermal conditions were experimentally defined for the investigated elements. The elements were analyzed without addition of chemical modifiers, using organometallic standards for the calibration. Forty-microliter samples were injected into the THFA. Gasoline samples were analyzed directly, while diesel fuel samples were diluted 1:4 with n-heptane. The following characteristic masses were obtained: 0.8 pg Cd, 6.4 pg Cr, 12 pg Cu, 17 pg Pb and 27 pg Ni. The limits of determination for gasoline samples were 0.13 μg/kg Cd, 0.4 μg/kg Cr, 0.9 μg/kg Cu, 1.5 μg/kg Pb and 2.5 μg/kg Ni. The corresponding limit of determination for diesel fuel samples was approximately four times higher for all elements. The element recovery was performed using the addition of organometallic compounds to gasoline and diesel fuel samples and was between 85 and 105% for all elements investigated.

Capabilities and limitations of different techniques in electrothermal atomic absorption spectrometry for direct monitoring of arsenic, cadmium and lead contamination of sea-water

Three atomization techniques for electrothermal atomic absorption spectrometry (ETAAS), namely, wall, platform and graphite probe have been tested and critically compared for the direct determination of arsenic, cadmium and lead in sea-water. The best analytical performance was obtained using totally pyrolytic graphite platforms inserted in pyrolytic graphite coated graphite tubes, peak height measurement mode and the addition of chemical modifier (10 µg of palladium as nitrate). For arsenic determination the modifier was injected together with the sample (WET mode), while for cadmium and lead determination the modifier was previously reduced to Pd0 by in situ thermal decomposition of the palladium nitrate (DRY mode). With regard to sample pre-treatment, the sea-water was injected directly onto the platform for arsenic measurements, while dilution with ultrapure water (1 + 1) was preferable for lead and a dilution (1 + 3) with 25% ammonium nitrate solution was needed for cadmium. The limits of detection (LODs) for the three toxic elements, relative to the real samples (undiluted sea-water) analysed, were 1.7 µg l–1 for arsenic, 1.0 µg l–1 for cadmium and 1.3 µg l–1 for lead. The recoveries obtained for all three metals in sea-water samples were 100 ± 5% using the recommended ETAAS procedures. The analytical performances of the proposed methods are given. Quantification limits observed (5 × LOD) warrant the application of these methods to direct monitoring and control of contaminated waters for arsenic, cadmium and lead. However, when ‘normal’ levels of the metals in sea-water have to be determined adequate preconcentration techniques are needed.

The effect of chemical modifiers on the interaction of a spin-labeled local anesthetic with human erythrocyte membranes

The role of electrostatic forces in the interaction between local anesthetics and phospholipid membranes has been well studied previously. The present work tested the hypothesis that the tertiary amine local anesthetics can also interact with charged groups that may be present on membrane proteins. The rotational mobility of a spin-labeled local anesthetic, 2-[ N-methyl- N-(2,2,6.6-tetramethylpiperi-dinooxyl)] ethyl p-hexyloxybenzoate, in erythrocyte membranes was found to decrease upon addition of chemical modifiers that react covalently with free amino groups of the membrane and decrease the concentration of the membrane's fixed positive charge. Reagents that did not react with free amino groups, or those that did react with amino groups but did not alter the net charge of the membrane, had no effect on the mobility of the spin-labeled local anesthetic. The decrease in the anesthetic's mobility found after reaction with amino-directed reagents was shown to be due to the attraction of the positively charged anesthetic to the modified site. The immobilization of the anesthetics was primarily due to modification of the membrane protein components. The immobilized anesthetics are most probably located at the inner surface of the membrane.